Starch, the essential constituents of which are linear amylose and branched amylopectin glucose polymers can be converted into simple sugars by an enzymatic process carried out in two stages: one stage of liquefaction of the starch and one stage of saccharification of the liquefied starch. In order to obtain a high conversion level of the starch, pullulanase (E.C. 3.2.1.41, α-dextrin 6-glucano-hydrolase also termed alpha-1,6-glucosidase) has been used to catalyse the hydrolysis of alpha-1,6-glucosidic bonds.
Pullulanase enzymes in the art include those known to have optimum activity at acidic pH as well as those known to have activity at alkaline pH. Pullulanases described in the art include pullulanase derived from a strain of Bacillus acidopullulyticus described as having an optimum activity at a pH of 4-5 at 60° C. (U.S. Pat. No. 4,560,651); pullulanase derived from Bacillus naganoensis described as having a maximum activity at a pH of about 5, measured at 60° C. and a maximum activity at a temperature of about 62.5° C., measured at a pH of 4.5 (U.S. Pat. No. 5,055,403); pullulanase derived from Bacillus sectorramus described as having an optimum pH at 5.0 to 5.5 and an optimum temperature at 50° C. (U.S. Pat. No. 4,902,622); and pullulanase derived from Bacillus brevis PL-1 described as having activity at 4.5-5.5 at 60° C. (JP 04/023985).
Pullulanase can be used with glucoamylase or β-amylase for the production of high glucose and high maltose syrups. In addition to increasing the yields of sugars, pullulanase reduces reaction time, allows high substrate concentrations and a reduction of up to 50% in the use of glucoamylase (Bakshi et al. (1992) Biotechnology Letters vol. 14 pp. 689-694).